In recent years, with progress of a hard disk device (which is hereinafter referred to as “HDD” in some cases) of a computer having high performance and reduced size, a 2.5-inch (63.5 mm) HDD is becoming mainstream, and furthermore, a small-sized HDD, such as 1.8 inch (45.7 mm) or 1 inch (25.4 mm), is becoming available as commercial products. The small-sized HDD has a complicated circuit structure and suffers failure with only a little dust, and therefore, dust is generally prevented from invading by using a gasket. A HDD gasket used for the small-sized HDD necessarily has a narrower line width and a large height, i.e., a gasket having a wall-like shape.
There are increasing cases where a HDD is used in a portable electronic equipment associated with the aforementioned reduction in size, and a HDD is often used in a severe environment as compared to conventional purposes, such as PC, and thus is necessarily assumed to be used in a high humidity and temperature environment.
Furthermore, associated with reduction in size of a hard disk device, there are cases where the top and bottom portions thereof, which are to be sealed with a gasket, are not in parallel to each other, and in these cases, the gasket receives a force in an oblique direction, whereby the gasket is toppled sideways or peeled off in some cases. Even though the top and bottom of the seal are in parallel to each other, the gasket may receive a force in an oblique direction upon screwing, which brings about the cases where the gasket is toppled sideways or peeled off. In particular, a gasket with a shape having a narrower line width and a large height for a small-seized hard disk device suffers the phenomenon conspicuously.
A gasket having a multi-stage shape is proposed for providing a gasket that satisfies the aforementioned required properties (see, for example, Patent Document 1). Specifically, the document discloses a gasket having a multi-stage shape formed by molding a gasket material containing an ultraviolet ray-curable elastomer with a dispenser, which exhibits excellent sealability for a prolonged period of time owing to the multi-stage cross sectional shape thereof. For preventing the gasket from being toppled sideways or peeled off with maintaining the sealability thereof under the high humidity and temperature environment, it is necessary to increase the adhesiveness to a cover plate and a base plate for protecting a HDD, which are described in detail later.
A HDD is protected with a protective member 1 containing a cover plate 11 and a base plate 12 as shown in FIG. 1. More specifically, the HDD is disposed on the base plate 12 and sealed with a gasket 13 holding with the cover plate 11 and the base plate 12.
The production yield of HDD is currently around 50%, and parts of a rejected product are necessarily regulated by the parts thereof after detaching the cover plate 11 from the base plate 12 as shown in FIG. 2 or FIG. 3. There are the case where the gasket is formed and adhered to the cover plate as shown in FIG. 2 and the case where it is formed and adhered to the base plate as shown in FIG. 3, and in either case, the gasket is stuck to the other plate to accomplish sealing. In the case where the cover plate 11 is detached from the base plate 12 upon regulating the parts of the HDD, it is desired that the stuck part is clearly peeled off with no gasket remaining, and the adhered part maintains the gasket staying.
However, the gasket having a multi-stage shape, which is firmly adhered to the cover plate and the base plate for maintaining the sealability of the gasket, is poor in reworkability and thus is problematic on regulating the HDD. The use of a material having a low adhering force in consideration of reworkability, on the other hand, results in insufficient sealability.
The term adhesion referred herein means that a gasket is firmly in contact closely with an adherend with chemical bond or the like through ultraviolet ray curing or the like, and the term sticking means that a gasket is physically in contact with an adherend with tackiness, heat, compression or the like of the gasket.    [Patent Document 1] JP-A-2003-120819